The present invention relates to a short-range radar system as well as a method for operating a short-range radar system.
From the state of the art, short-range radar systems for various automobile uses are known. The corresponding radar sensors operate according to the pulse-echo principle: an electromagnetic pulse of approximately 400 ps duration is emitted from the radar sensor; in the area surrounding the vehicle, the pulse contacts another vehicle, a limiting wall, or another obstacle, for example. The pulse reflected on the obstacle is detected and evaluated. The running time of the pulses and the frequency shift based on the Doppler Effect are the essential measured quantity, from which the distance and relative speed are determined.
At very close range, the pulse-echo measurement is operated with a center frequency of approximately 24 GHz. In this manner, the detection range around the sensor is subdivided into spherical layers, which are designated as “range gates”. These “range gates” have a width of approximately 20 cm and are sensed by a pulse sequence. Within approximately 10 ms, the entire detection range is measured in the vehicle surrounding area in this manner.
From the state of the art, known uses for short-range radar sensor systems, for example, are parking assistance, collision forecasts, successive methods, tracking change assistance, and adaptive cruise control. Corresponding SRR radar sensor systems are available commercially available from the firm Robert Bosch GmbH, Stuttgart.
FIG. 1 shows a prior art HF-impulse generator 1, such as those that are used in commercially available short-range radar systems of the firm Robert Bosch GmbH. The HF-impulse generator 1 is closed or terminated by a high ohmic resistor 3 of 1.8 kΩ or 2.7 kΩ, for example.
If a corresponding control signal is emitted from a control apparatus 4 in the input 5 of the HF-impulse generator, this provides at its output 6 an HF-impulse of a predetermined pulse duration typically of 400 ps. This HF-impulse is input into the HF-switch 7.
The high ohmic resistor causes the current, which the switch diodes demodulate based on the negative pulse, to cause a positive voltage by means of this resistor. This voltage, the so-called back-bias voltage, suppresses the diodes, as long as no pulse is applied. If a negative pulse is injected, first the back-bias voltage is overcome and then the diodes are connected through.
FIG. 2 shows the voltage variation of a corresponding impulse for a resistor 3 of 2.7 kΩ. The diodes switch gate is −0.6 V, from which the resulting HF-pulse width is provided.
The short range around the motor vehicle, then, is sensed with a stable HF-pulse width 8. The achievable range of distance amounts to 7 m, for example.
An object of the present invention is to produce a short-range radar system with an enlarged range of distance.